This invention relates to a seat drive device suitable for use in automotive vehicles.
There is known a seat slide device for automotive vehicles as disclosed in Japanese Patent Unexamined Publication (Kokai) No. Hei 9-48268. This conventional seat slide device for automotive vehicles comprises, as shown in FIG. 4, a lower rail 100 having a generally U-shaped configuration when viewed in a direction of an end view thereof and an upper rail 108 and a generally L-shaped configuration. The lower rail 100 includes side wall portions 102 formed by bending two side portions of a horizontal bottom wall portion 101 upwardly, a top wall portion 103 formed by bending upper end portions of the side wall portions 102 inwardly in opposing directions like a fishing hook, and vertically downwardly-extended wall portions 104. The upper rail 108 is comprised of a pair of generally L-shaped plates W, Z each of which includes a horizontal wall portion 106 which is bent like a fishing hook from a lower end portion of a vertical wall portion 105 and a raised wall portion 107, the pair of L-shaped plates W, Z being abutted with each other at the back sides of the vertical wall portions 105 and formed as one piece. The upper rail is slidably fitted to the lower rail such that the raised wall portions 107 of the upper rail 108 are located between the side wall portions 102 of the lower rail 100 and the downwardly-extended wall portions 104. A lock plate 110 capable of engaging one of the engagement toothed portions 109 formed on the downwardly-extended wall portions 104 of the lower rail is abutted with one side surface of the vertical wall portion 105 so that an upper portion of the vertical wall portion 105 of one W of the L-shaped plates constituting the upper rail 108 can be served also as a seat cushion attachment bracket.
Such a seat slide device of rail type having a T-shaped configuration in section is demanded to have such features that from a view point of obtaining physical strength, it has, when viewed in a direction of an end face thereof, a laterally symmetrical configuration with respect to a vertical center line, the upper rail and the lock plate abutted with the upper rail are located in a central position of the lower rail, and there is adopted such an impact-load countermeasure applicable to the seat belt attachment portion when a vehicle collision or the like occurs that an engagement portion between the engagement toothed portion formed on the lower rail and the lock plate is located outwardly of the vertical center line serving as a fulcrum.
In order to fulfill the above demands, the prior art device adopted the following impact-load countermeasure. The width of the lower rail and the distance between the two downwardly-extended wall portions of the lower rail are reduced. The upper rail and the lock plate abutted with the upper rail are located in the central position of the lower rail, and a portion of the horizontal wall portion of the upper rail where the lock plate is engaged with the engagement toothed portion of the lower rail is formed short.
However, the above prior art device has the following inconveniences. Since the two horizontal walls of the L-shaped plates of the upper rail are different in length, the horizontal wall portion having a longer length dimension is readily warped and susceptible to one-sided deformation. Since the lower rail is reduced in width, machining and assembling work is disturbed. Moreover, since the two L-shaped plates are different in configuration and one of the L-shaped plates is served also as a seat attachment bracket, they must be separately made at the left and right sides of the seat and therefore, favorable productivity is difficult to obtain.